The present invention relates broadly to dental adhesives and, more specifically, to orthodontic adhesives suitable for use in adhering orthodontic appliances to human teeth.
Prior to the 1970's, orthodontic appliances were commonly attached to teeth by stainless steel bands which circumscribed the entire tooth. These appliances were painful and tedious to fit, and often painful and cumbersome to wear. Furthermore, these appliances quite often resulted in the formation of pre-carious lesions in the tooth enamel beneath the bands during the course of treatment. These lesions were caused because of microleakage of the luring cement used to fill any voids between the band and the tooth surface, due to the impossible difficulties of perfectly adapting the band to the contours of the tooth surface. At this time, orthodontic appliances were developed in the form of buccal, and later also lingual, brackets with flat or slightly contoured bases, which could be adhered to an etched tooth surface with self-curing polymeric resinous adhesives.
Later, in the early 1970's, with the development of the first photocurable dental materials, disclosed in U.S. Pat. Nos. 3,629,187 and 3,709,866, it became possible to utilize photocurable orthodontic adhesives in addition to the self-curing type. The photocured material required that the orthodontic appliances or brackets were sufficiently perforated to permit the rays from the curing light to pass through the bracket, and effect adequate polymerization curing of the adhesive interlayer to ensure strong adherence to the etched tooth surface and to the base of the bracket, since such adherence is only as strong as the weakest interface. U.S. Pat. No. 4,063,360 sets forth an example of the state of the art at this time.
Since the early 1970's, there has been considerable technical progress in all associated areas, including the development, and in many cases, commercialization of new raw materials suitable for the formulation of orthodontic adhesives, the design of orthodontic appliances, and of dental curing lights.
Some of these developments which impact the present invention are the synthesis and commercialization of Ethoxylated Bisphenol A Dimethacrylate resin, the interest in urethane chemistry, which led to the synthesis of the urethane polymethacrylate resins described in U.S. Pat. No. 4,554,336, the development of fluoride leachable glasses described in U.S. Pat. No. 4,746,686, and the synthesis of fluorine-containing adducts such as described in U.S. Pat. No. 4,772,325.
There is a continuing need in the dental field for orthodontic adhesives, both visible light curable and self-curing, which can firmly adhere orthodontic appliances to the dentition, and which provide for a high degree of surface wetting, which contain an available source of leachable fluoride, and which have low polymerization shrinkage and high physical properties. These compositions should include either photoinitiators or self-curing catalysts, and optionally a combination of both, to provide a degree of post-curing capability, together with a polymerizable liquid matrix and a high loading of filler(s) to significantly reduce polymerization shrinkage. They should further provide a thixotropic, taffy-like consistency for optimal manipulation, prior to polymerization curing.
It is therefore an objective of the present invention to provide superior state of the art orthodontic adhesives of both the visible light curable and self-curing types having the properties and advantages described above.